The Epidemiologic

Triangle

Contagion

Epidemiology: What is it?

• Epi – means “on, upon, befall” (ex: epidermis)• Demo – means “people” (ex: demographics, the

study of populations)• -ology – means “the study of”(ex: biology, geology)• So, epidemiology literally translates to “the study

of that which befalls people”• Epidemiology – learning how diseases are

distributed in a certain place and time

John Snow: The First Epidemiologist

• Read “Finding the Real Cause of Cholera” with your table.

• What did John Snow think was causing the cholera outbreak?

• How do you think John Snow proved his theory using the scientific method?

John Snow: The First Epidemiologist

• Read “John Snow’s Methods”– How did John

Snow prove that cholera was being spread by contaminated water?

Epidemiology• The Center for Disease Control (CDC) uses a

model called the Epidemiologic Triangle to pinpoint outbreaks of infectious diseases

TIME

HOST

ENVIRONMENTAGENT

The triangle has three vertices:• Agent, or microbe that

causes the disease (the “What” of the triangle

• Host, or organism harboring the disease (the “who” of the triangle)

• Environment, or those external factors that cause or allow disease transmission (the “where”)

The center of the triangle is TIME – this is what epidemiologists are working against

Outbreaks, Epidemic vs. Endemic• An outbreak or epidemic exists when there are

more cases of a particular disease than expected in a given area, or among a specific group of people, over a particular time. – Example: Seasonal flu

• Endemic means a population has a high level of disease all the time. – Example: Malaria is endemic in Africa

Example Case Study: Varicella zoster (chickenpox)

HOST

ENVIRONMENTAGENT

Varicella zoster, a virus

People under 15 most at riskAnyone who hasn’t had it is susceptibleCan remain in the body and cause shingles (painful blisters) in adults

Transmitted from an infected person through coughs or sneezes, or from contact with the fluid from chickenpox blistersMost commonly transmitted in the early winter or spring, when temperatures are moderate

Mystery Disease• Watch the following clip: Mystery Disease• While watching, look for the following

epidemiological clues:– How might it be spreading? (Agent)– Who/what is getting disease? (Host)– Where is it happening? (Environment)

Mystery Solved!• Let’s see if you were right… Mystery Solved

Public Service Announcement Skits

• Working in your table groups, use the information from the case study provided to create a Public Service Announcement skit about your disease.

• It can be a radio broadcast, TV commercial, talk show interview, etc… be creative!

• In your skit, include…– The epidemiological triangle for how your disease is transmitted, including time-What people should doavoid getting disease

TIME

HOST

ENVIRONMENTAGENT

Common Infectious Diseases (HW or Classroom Activity)

I’ve Had Family Members Have Had

Heard About

Compare the diseases you’ve had, and diseases your family has had with your table. What diseases do you have in common? What diseases did your family have that you haven’t had? Why do you think this is? What are some diseases you’ve heard about, but don’t know anyone who has had that disease?